Golden gold powder precipitated... Is this gold?

[LT_golden]

So I didn't remove as much base metals as I could/should have, due to mistakes (spraying down filter with water instead of HCl for pins with solder, processed filters from different leaching processes together, etc.)... but I did manage to get rid of much of the base metals, before dissolving everything else in Poor Man's Aqua Regia. I knew that to get any respectable purity I would have to re-refine, which I was planning to do anyways.

In the dirty soup I had, the base metals were tin, composites of kovar, and copper. The precious metals (that I care about) were silver and gold.

The solution tested nicely positive for gold, so in my excitement (and sleepiness at the time), I went ahead with adding urea to deNOx. Halfway through, I remembered the senior forum members' advice and just stopped and decided to go to bed. Later on, I went with evaporating and adding of HCl to remove excess nitric. After like 3 loops of this, I started adding SMB to precipitate the gold:





Whoa...! This was beautiful but alarming... Did I really precipitate gold? The particles actually were large enough to be seen as a golden color? It seemed almost... wrong. I let it settle overnight, decanted, and set the powders to force evaporate just a bit before doing HCl washes.





In the solution which now tested negative for gold, there also seemed to be many iridescent particles floating around and not settling even after several hours. These only appeared after the previously mentioned addition of SMB to precipitate gold. The solution also showed the Tyndall effect which, coupled with the brownish-red color, made me think that there was colloidal gold.





So I poured out 100 mL for testing... Evaporating down to syrup, adding HCl and H₂O₂ to force stannous into stannic and re-dissolve the gold... repeated a few times... Still the solution tested negative for gold. So I stored the solution for later processing. I did this based on comments by Goran and Geo in this thread:

Just as a test I once dripped some stannous into a gold chloride solution. I still had some oxidizer left so all I needed to do was to stir it a bit to get the ruby red gold colloid to dissolve again.

Agreed. Add more oxidizer until the solution clears. Enough oxidizer will overpower the tin.

I will wait until I can evaporate & incinerate more safely before processing that solution.


My questions are...

1. Did I really precipitate golden gold powder?! I'm also washing with HCl / water / ammonium hydroxide boils so I guess this question will answer itself later...
2. I took out a smaller sample of the solution and added some H₂O₂, and the color actually lightened. Might this just have been the dilution causing the color to lighten? Because when I did the HCl + H₂O₂ to remove the nitric acid, the bulk solution didn't lighten...
3. Could the iridescent glittering and the Tyndall effect be actually due to silver chloride, in both nano-sized and macro-sized particles?
4. Did I do it right with the process to try and fix the solution suspected to contain colloidal gold?

Thanks for all y'all's input...

 

[Lino1406]

Normmally l would prefer stannous tin over stannic oxide, so the reverse artitude is not acceptable by me

 

[anachronism]

To answer your question yes you dropped metallic gold.

That given gold powder in its brown form is also metallic.

The only times I've done this have been when certain pH levels have been present. For some reason it's when the pH is higher if I recall correctly. It's rare- only 5 times in nearly 7 years refining so far.

I had to grab this pic the other night because it was quite a big drop and as you said it's really pretty.

 

[Geo]

I've seen it happen when I dropped gold that came from a sulfuric stripping cell.

 

[LT_golden]

Hi anachronism,

To answer your question yes you dropped metallic gold.

I had to grab this pic the other night because it was quite a big drop and as you said it's really pretty.

Wow, yeah, that's really pretty...! I have no idea how I did it. I didn't check or adjust the pH, I only added a good amount (unmeasured) of urea first from a left-over instant cold pack, and also from the bottle from the chemistry store because there was still fizzing.

Have you noticed that this golden gold powder precipitate seems to flocculate less? I let my powder settle overnight, but in the morning, there was still a centimeter-thick layer of glittering powder that seems to be in suspension. Also when I swirled the beaker a little, the powder didn't seem to willingly swirl towards the center, and a little powder actually drifted towards the top.

This is even more obvious when I heated the solution... A very thin film of powder would form, which is difficult to spray down. I was disinclined to think that it was because of oils, because...

This was how I cleaned my beaker:

• Soak in ~15% HCl overnight, rinse with distilled water;
• Wipe down insides with 95% ethanol while wearing gloves, rinse with distilled water;
• Soak in sodium hydroxide solution overnight, rinsing with distilled water;
• Soak in distilled water overnight.

By this point, water no longer formed droplets on the inside or outside of the beaker; water would be a really thin film that just kept flowing.

This was how I washed the golden powder:

• Simmer golden powder in ~20% HCl for ~30 minutes, decant. Solution was light orange-ish.
• Simmer in distilled water, decant. Solution was even lighter shade of orange.
• Simmer in ammonium hydroxide, decant. Solution was a darker orange than when simmering with HCl.
• Simmer in distilled water. No color in solution when decanting.

During each pour, a small amount of powder would refuse to sink down, so I had to just decant through a Charmin plug. This filtered so well that the solution was completely clear of any suspended particles.

At the end of the wash, there was still floating powder, and I thought I might've just not simmered it enough, so I re-simmered in HCl for over an hour, but there was no color change at all, and the powders remained floating despite swirling efforts. Throughout the simmer there seemed to be no reaction going on, no bubbling, nothing seemed to have dissolved.

Also I'm having a really hard time force-drying the powders. I read that you're supposed to keep tapping the beaker so the powder keeps moving, but I could never get it to move after it's dried to a certain... dryness, and the fine powders just stayed higher up on the inside after all the movement and refused to move. A quick spray easily moved the powders, though, so they're not really "stuck" by something like grease, I guess.





I will be re-refining this (including the Charmin plug paper) later so it's not a huge deal I guess, but still somewhat annoying. From videos, it seems that the normal brown gold powder is easier to handle/settle/flocculate.

So my questions are:

• In your experiences, do you find that this golden gold powder is harder to handle? Perhaps due to minute air particles trapped inside?
• How do I force dry the powder so that it collects loosely instead of sticking to the beaker?

Thanks for all of y'all's help.

 

[Platdigger]

Has anyone ever used a flocculant for such a situation?
I realize you would be adding or introducing another metal or metal ions to the solution,
but it should only be a tiny amount, and shouldn't make much difference if you are going to redissolve and drop again anyway.

Alum is one or FeSO4 (iron(11) sulfate) is another as for instance.

 

[Geo]

Adding dilute sulfuric acid and a good boil will make it settle.

 

[g_axelsson]

Whenever I have a problematic precipitation that is too fine or something like that I never mess with it. What I do is...

- Let it settle enough to decant most of the liquid.
- Add HCL and bleach or strong peroxide to dissolve most of the gold again, easy to do when the gold is in a fine powder.
- Add SMB to drop the gold again.

You don't need to dissolve everything, the finer gold particles are the problematic ones and will dissolve first. By using less than needed oxidizer for the gold there will be no excess oxidizer, so no need for removing any excess oxidizer. And if the solution looks clear I never filter the solution before dropping it again. The second drop has never been problematic for me and dissolving, dropping and starting to wash can be done within an hour. It saves time and anguish.

That golden snow globe effect is pretty but could be problematic.

Göran

 

[g_axelsson]

By the way, this is not colloidal gold, if it twinkles then it has to be large flat surfaces way bigger than the length of a light wave. Since we can see the particles as spots it's probably in the 1/10-1/100 of a mm in size. Very thin flat crystals of gold, more like snow flakes than the normal hail form that drops fast to the bottom and doesn't move.

Göran